Ha! I have a supersmart friend. So smart, he got his MBA and his JD from two top universities in three years concurrently, by cobbling together his own program. That's some seriously creative DIY. He always thought this word meant the opposite until someone called him out early in his career. I always smile inwardly and think of him (and his wildly successful career) when I hear this word.
Omg, this reminds me of my father, who is well educated and phenomenally well read, but English isn't his first language, so there are a few words floating around in his mental compendium that trip him up. To this day, no matter how many times I correct him, he still thinks that "perfunctory" is somehow related to "perfectionism."
Of course, he likes his own reality better than everyone else's, so it's not so much a matter of him being unable to understand that he's wrong, but more that he's unwilling, and doesn't consider respecting the true meaning of "perfunctory" to be important to him.
He's a character that one. He also likes to lob fake facts into the universe just for fun, it makes talking to him a bit treacherous since he's so incredibly well informed, he can easily hide a made up fact within a long, well supported discourse on anything.
The dude is kind of nuts.